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+/*
+** Copyright (c) 2020 D. Richard Hipp
+**
+** This program is free software; you can redistribute it and/or
+** modify it under the terms of the Simplified BSD License (also
+** known as the "2-Clause License" or "FreeBSD License".)
+**
+** This program is distributed in the hope that it will be useful,
+** but without any warranty; without even the implied warranty of
+** merchantability or fitness for a particular purpose.
+**
+** Author contact information:
+**   drh@hwaci.com
+**   http://www.hwaci.com/drh/
+**
+*******************************************************************************
+**
+** This file contains subroutines used for recognizing, configuring, and
+** handling interwiki hyperlinks.
+*/
+#include "config.h"
+#include "interwiki.h"
+
+
+/*
+** If zTarget is an interwiki link, return a pointer to a URL for that
+** link target in memory obtained from fossil_malloc().  If zTarget is
+** not a valid interwiki link, return NULL.
+**
+** An interwiki link target is of the form:
+**
+**       Code:PageName
+**
+** "Code" is a brief code that describes the intended target wiki.
+** The code must be ASCII alpha-numeric.  No symbols or non-ascii
+** characters are allows.  Case is ignored for the code.
+** Codes are assigned by "intermap:*" entries in the CONFIG table.
+** The link is only valid if there exists an entry in the CONFIG table
+** that matches "intermap:Code".
+**
+** Each value of each intermap:Code entry in the CONFIG table is a JSON
+** object with the following fields:
+**
+**    {
+**      "base":  Base URL for the remote site.
+**      "hash":  Append this to "base" for Hash targets.
+**      "wiki":  Append this to "base" for Wiki targets.
+**    }
+**
+** If the remote wiki is Fossil, then the correct value for "hash"
+** is "/info/" and the correct value for "wiki" is "/wiki?name=".
+** If (for example) Wikipedia is the remote, then "hash" should be
+** omitted and the correct value for "wiki" is "/wiki/".
+**
+** PageName is link name of the target wiki.  Several different forms
+** of PageName are recognized.
+**
+**    Path       If PageName is empty or begins with a "/" character, then
+**               it is a pathname that is appended to "base".
+**
+**    Hash       If PageName is a hexadecimal string of 4 or more
+**               characters, then PageName is appended to "hash" which
+**               is then appended to "base".
+**
+**    Wiki       If PageName does not start with "/" and it is
+**               not a hexadecimal string of 4 or more characters, then
+**               PageName is appended to "wiki" and that combination is
+**               appended to "base".
+**
+** See https://en.wikipedia.org/wiki/Interwiki_links for further information
+** on interwiki links.
+*/
+char *interwiki_url(const char *zTarget){
+  int nCode;
+  int i;
+  const char *zPage;
+  int nPage;
+  char *zUrl = 0;
+  char *zName;
+  static Stmt q;
+  for(i=0; fossil_isalnum(zTarget[i]); i++){}
+  if( zTarget[i]!=':' ) return 0;
+  nCode = i;
+  if( nCode==4 && strncmp(zTarget,"wiki",4)==0 ) return 0;
+  zPage = zTarget + nCode + 1;
+  nPage = (int)strlen(zPage);
+  db_static_prepare(&q,
+     "SELECT value->>'base', value->>'hash', value->>'wiki'"
+     " FROM config WHERE name=lower($name) AND json_valid(value)"
+  );
+  zName = mprintf("interwiki:%.*s", nCode, zTarget);
+  db_bind_text(&q, "$name", zName);
+  while( db_step(&q)==SQLITE_ROW ){
+    const char *zBase = db_column_text(&q,0);
+    if( zBase==0 || zBase[0]==0 ) break;
+    if( nPage==0 || zPage[0]=='/' ){
+      /* Path */
+      zUrl = mprintf("%s%s", zBase, zPage);
+    }else if( nPage>=4 && validate16(zPage,nPage) ){
+      /* Hash */
+      const char *zHash = db_column_text(&q,1);
+      if( zHash && zHash[0] ){
+        zUrl = mprintf("%s%s%s", zBase, zHash, zPage);
+      }
+    }else{
+      /* Wiki */
+      const char *zWiki = db_column_text(&q,2);
+      if( zWiki && zWiki[0] ){
+        zUrl = mprintf("%s%s%s", zBase, zWiki, zPage);
+      }
+    }
+    break;
+  }
+  db_reset(&q);
+  free(zName);
+  return zUrl;
+}
+
+/*
+** If hyperlink target zTarget begins with an interwiki tag that ought
+** to be excluded from display, then return the number of characters in
+** that tag.
+**
+** Path interwiki targets always return zero.  In other words, links
+** of the form:
+**
+**       remote:/path/to/file.txt
+**
+** Do not have the interwiki tag removed.  But Hash and Wiki links are
+** transformed:
+**
+**       src:39cb0a323f2f3fb6  ->  39cb0a323f2f3fb6
+**       fossil:To Do List     ->  To Do List
+*/
+int interwiki_removable_prefix(const char *zTarget){
+  int i;
+  for(i=0; fossil_isalnum(zTarget[i]); i++){}
+  if( zTarget[i]!=':' ) return 0;
+  i++;
+  if( zTarget[i]==0 || zTarget[i]=='/' ) return 0;
+  return i;
+}
+
+/*
+** Verify that a name is a valid interwiki "Code".  Rules:
+**
+**     *    ascii
+**     *    alphanumeric
+*/
+static int interwiki_valid_name(const char *zName){
+  int i;
+  for(i=0; zName[i]; i++){
+    if( !fossil_isalnum(zName[i]) ) return 0;
+  }
+  return 1;
+}
+
+/*
+** COMMAND: interwiki*
+**
+** Usage: %fossil interwiki COMMAND ...
+**
+** Manage the "intermap" that defines the mapping from interwiki tags
+** to complete URLs for interwiki links.
+**
+** > fossil interwiki delete TAG ...
+**
+**        Delete one or more interwiki maps.
+**
+** > fossil interwiki edit TAG --base URL --hash PATH --wiki PATH
+**
+**        Create an interwiki referenced call TAG.  The base URL is
+**        the --base option, which is required.  The --hash and --wiki
+**        paths are optional.  The TAG must be lower-case alphanumeric
+**        and must be unique.  A new entry is created if it does not
+**        already exit.
+**
+** > fossil interwiki list
+**
+**        Show all interwiki mappings.
+*/
+void interwiki_cmd(void){
+  const char *zCmd;
+  int nCmd;
+  db_find_and_open_repository(0, 0);
+  if( g.argc<3 ){
+    usage("SUBCOMMAND ...");
+  }
+  zCmd = g.argv[2];
+  nCmd = (int)strlen(zCmd);
+  if( strncmp(zCmd,"edit",nCmd)==0 ){
+    const char *zName;
+    const char *zBase = find_option("base",0,1);
+    const char *zHash = find_option("hash",0,1);
+    const char *zWiki = find_option("wiki",0,1);
+    verify_all_options();
+    if( g.argc!=4 ) usage("add TAG ?OPTIONS?");
+    zName = g.argv[3];
+    if( zBase==0 ){
+      fossil_fatal("the --base option is required");
+    }
+    if( !interwiki_valid_name(zName) ){
+      fossil_fatal("not a valid interwiki tag: \"%s\"", zName);
+    }
+    db_begin_write();
+    db_unprotect(PROTECT_CONFIG);
+    db_multi_exec(
+       "REPLACE INTO config(name,value,mtime)"
+       " VALUES('interwiki:'||lower(%Q),"
+              " json_object('base',%Q,'hash',%Q,'wiki',%Q),"
+              " now());",
+       zName, zBase, zHash, zWiki
+    );
+    setup_incr_cfgcnt();
+    db_protect_pop();
+    db_commit_transaction();
+  }else
+  if( strncmp(zCmd, "delete", nCmd)==0 ){
+    int i;
+    verify_all_options();
+    if( g.argc<4 ) usage("delete ID ...");
+    db_begin_write();
+    db_unprotect(PROTECT_CONFIG);
+    for(i=3; i<g.argc; i++){
+      const char *zName = g.argv[i];
+      db_multi_exec(
+        "DELETE FROM config WHERE name='interwiki:%q'",
+        zName
+      );
+    }
+    setup_incr_cfgcnt();
+    db_protect_pop();
+    db_commit_transaction();
+  }else
+  if( strncmp(zCmd, "list", nCmd)==0 ){
+    Stmt q;
+    int n = 0;
+    verify_all_options();
+    db_prepare(&q,
+      "SELECT substr(name,11),"
+      "       value->>'base', value->>'hash', value->>'wiki'"
+      "  FROM config WHERE name glob 'interwiki:*' AND json_valid(value)"
+    );
+    while( db_step(&q)==SQLITE_ROW ){
+      const char *zBase, *z, *zName;
+      if( n++ ) fossil_print("\n");
+      zName = db_column_text(&q,0);
+      zBase = db_column_text(&q,1);
+      fossil_print("%-15s %s\n", zName, zBase);
+      z = db_column_text(&q,2);
+      if( z ){
+        fossil_print("%15s %s%s\n", "", zBase, z);
+      }
+      z = db_column_text(&q,3);
+      if( z ){
+        fossil_print("%15s %s%s\n", "", zBase, z);
+      }
+    }
+    db_finalize(&q);
+  }else
+  {
+     fossil_fatal("unknown command \"%s\" - should be one of: "
+                  "delete edit list", zCmd);
+  }
+}
+
+
+/*
+** Append text to the "Markdown" or "Wiki" rules pages that shows
+** a table of all interwiki tags available on this system.
+*/
+void interwiki_append_map_table(Blob *out){
+  int n = 0;
+  Stmt q;
+  db_prepare(&q,
+    "SELECT substr(name,11), value->>'base'"
+    "  FROM config WHERE name glob 'interwiki:*' AND json_valid(value)"
+    " ORDER BY name;"
+  );
+  blob_append(out, "<blockquote>", -1);
+  while( db_step(&q)==SQLITE_ROW ){
+    if( n==0 ){
+      blob_appendf(out, "<table>\n");
+    }
+    blob_appendf(out,"<tr><td>%h</td><td>&nbsp;&rarr;&nbsp;</td>",
+       db_column_text(&q,0));
+    blob_appendf(out,"<td>%h</td></tr>\n",
+       db_column_text(&q,1));
+    n++;
+  }
+  db_finalize(&q);
+  if( n>0 ){
+    blob_appendf(out,"</table></blockquote>\n");
+  }else{
+    blob_appendf(out,"<i>None</i></blockquote>\n");
+  }
+}
+
+/*
+** WEBPAGE: intermap
+**
+** View and modify the interwiki tag map or "intermap".
+** This page is visible to administrators only.
+*/
+void interwiki_page(void){
+  Stmt q;
+  int n = 0;
+  const char *z;
+  const char *zTag = "";
+  const char *zBase = "";
+  const char *zHash = "";
+  const char *zWiki = "";
+  char *zErr = 0;
+
+  login_check_credentials();
+  if( !g.perm.Read && !g.perm.RdWiki && ~g.perm.RdTkt ){
+    login_needed(0);
+    return;
+  }
+  if( g.perm.Setup && P("submit")!=0 && cgi_csrf_safe(2) ){
+    zTag = PT("tag");
+    zBase = PT("base");
+    zHash = PT("hash");
+    zWiki = PT("wiki");
+    if( zTag==0 || zTag[0]==0 || !interwiki_valid_name(zTag) ){
+      zErr = mprintf("Not a valid interwiki tag name: \"%s\"", zTag?zTag : "");
+    }else if( zBase==0 || zBase[0]==0 ){
+      db_unprotect(PROTECT_CONFIG);
+      db_multi_exec("DELETE FROM config WHERE name='interwiki:%q';", zTag);
+      db_protect_pop();
+    }else{
+      if( zHash && zHash[0]==0 ) zHash = 0;
+      if( zWiki && zWiki[0]==0 ) zWiki = 0;
+      db_unprotect(PROTECT_CONFIG);
+      db_multi_exec(
+        "REPLACE INTO config(name,value,mtime)"
+        "VALUES('interwiki:'||lower(%Q),"
+        " json_object('base',%Q,'hash',%Q,'wiki',%Q),"
+        " now());",
+        zTag, zBase, zHash, zWiki);
+      db_protect_pop();
+    }
+  }
+
+  style_set_current_feature("interwiki");
+  style_header("Interwiki Map Configuration");
+  @ <p>Interwiki links are hyperlink targets of the form
+  @ <blockquote><i>Tag</i><b>:</b><i>PageName</i></blockquote>
+  @ <p>Such links resolve to links to <i>PageName</i> on a separate server
+  @ identified by <i>Tag</i>.  The Interwiki Map or "intermap" is a mapping
+  @ from <i>Tags</i> to complete Server URLs.
+  db_prepare(&q,
+    "SELECT substr(name,11),"
+    "       value->>'base', value->>'hash', value->>'wiki'"
+    "  FROM config WHERE name glob 'interwiki:*' AND json_valid(value)"
+  );
+  while( db_step(&q)==SQLITE_ROW ){
+    if( n==0 ){
+      @ The current mapping is as follows:
+      @ <ol>
+    }
+    @ <li><p> %h(db_column_text(&q,0))
+    @ <ul>
+    @ <li> Base-URL: <tt>%h(db_column_text(&q,1))</tt>
+    z = db_column_text(&q,2);
+    if( z==0 ){
+      @ <li> Hash-path: <i>NULL</i>
+    }else{
+      @ <li> Hash-path: <tt>%h(z)</tt>
+    }
+    z = db_column_text(&q,3);
+    if( z==0 ){
+      @ <li> Wiki-path: <i>NULL</i>
+    }else{
+      @ <li> Wiki-path: <tt>%h(z)</tt>
+    }
+    @ </ul>
+    n++;
+  }
+  db_finalize(&q);
+  if( n ){
+    @ </ol>
+  }else{
+    @ No mappings are currently defined.
+  }
+
+  if( !g.perm.Setup ){
+    /* Do not show intermap editing fields to non-setup users */
+    style_finish_page();
+    return;
+  }
+
+  @ <p>To add a new mapping, fill out the form below providing a unique name
+  @ for the tag.  To edit an exist mapping, fill out the form and use the
+  @ existing name as the tag.  To delete an existing mapping, fill in the
+  @ tag field but leave the "Base URL" field blank.</p>
+  if( zErr ){
+    @ <p class="error">%h(zErr)</p>
+  }
+  @ <form method="POST" action="%R/intermap">
+  login_insert_csrf_secret();
+  @ <table border="0">
+  @ <tr><td class="form_label" id="imtag">Tag:</td>
+  @ <td><input type="text" id="tag" aria-labeledby="imtag" name="tag" \
+  @ size="15" value="%h(zTag)"></td></tr>
+  @ <tr><td class="form_label" id="imbase">Base&nbsp;URL:</td>
+  @ <td><input type="text" id="base" aria-labeledby="imbase" name="base" \
+  @ size="70" value="%h(zBase)"></td></tr>
+  @ <tr><td class="form_label" id="imhash">Hash-path:</td>
+  @ <td><input type="text" id="hash" aria-labeledby="imhash" name="hash" \
+  @ size="20" value="%h(zHash)">
+  @ (use "<tt>/info/</tt>" when the target is Fossil)</td></tr>
+  @ <tr><td class="form_label" id="imwiki">Wiki-path:</td>
+  @ <td><input type="text" id="wiki" aria-labeledby="imwiki" name="wiki" \
+  @ size="20" value="%h(zWiki)">
+  @ (use "<tt>/wiki?name=</tt>" when the target is Fossil)</td></tr>
+  @ <tr><td></td>
+  @ <td><input type="submit" name="submit" value="Apply Changes"></td></tr>
+  @ </table>
+  @ </form>
+
+  style_finish_page();
+}